Middlesbrough have received a timely boost ahead of Sunday's Premier League derby clash at Sunderland as centre-back Daniel Ayala could make an unexpected return to contention.

Ayala, 25, did not feature in any of Boro's pre-season friendlies due to an ankle injury that kept him out of the 1-1 home draw against Stoke on the opening day and boss Aitor Karanka was forced to play Antonio Barragan, bought in the summer from Valencia primarily as a right-back, in central defence.

Karanka is actively looking to bring in a new central defender and Boro have failed with a recent bid for Hull's Harry Maguire, but Ayala has returned to full training and Karanka confirmed the Spaniard is available for selection.

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'He has been training with us for the last two or three weeks, and he played 45 minutes and was working last week with the under-21s,' Karanka said.

'That's good news because he is a player that I can now add to the squad. Everyone knows how important Dani is for the team.

'He's been training and playing, so it is my decision (about whether to start him) now.'

Barragan was one of four summer signings to make their Boro debuts against Stoke alongside goalkeeper Victor Valdes, midfielder Marten de Roon and striker Alvaro Negredo, while Karanka was also impressed with those players who helped the club climb out of the Sky Bet Championship last season.

Karanka was pleasantly surprised by the performance of his players against Stoke City

MIDDLESBROUGH'S SUMMER SIGNINGS

Marten De Roon (Atalanta, £12m)

Viktor Fischer (Ajax, £3.8m)

Antonio Barragan (Valencia, £3m)

Fabio da Silva (Cardiff City, undisclosed)

Victor Valdes (Manchester United, free)

Brad Guzan (Aston Villa, free)

Bernardo Espinosa (Sporting Gijon, free)

Jordan McGhee (Hearts, loan)

Alvaro Negredo (Valencia, loan)

'Last week was good because some players showed they are better than I thought,' Karanka said.

'It was a pleasant surprise as I knew how good they are and were in the past, and working since the beginning of pre-season has been good. We're looking forward to Sunday.'

Boro have only won one of their last seven meetings with Sunderland, but that was in their most recent encounter in October 2012 when they beat them 1-0 at the Stadium of Light in the League Cup.

Karanka acknowledged Sunday's Wear-Tees derby was hugely important for the clubs' fans but would be approached in exactly the same way as any other league game.

Middlesbrough have only beaten Sunderland once in their last seven meetings

'It's a derby, but it's three points for us, and we don't have a lot of experience in these games,' he said.

'We don't have experience in the Premier League either, but as players and coaches we've played them, and we know there's something more.

'Everyone is ready and looking forward to the game. I don't think we and the rest of the teams are 100 per cent and the most important thing at this stage is points.

'It's a derby and for that reason it's important. It's the mentality I have to transmit to the players as we have another game the following Sunday - so we need to keep adding points.'

Marten De Roon (left) will not feature against Sunderland after injuring his hamstring

Karanka confirmed captain Grant Leadbitter remains sidelined following his hernia operation earlier this summer and that fellow midfielder De Roon would be out for two weeks due to the hamstring injury sustained on his league debut against Stoke.

Their absence could mean a Premier League start for Adam Forshaw, five years after appearing for Everton as a substitute in his only other top-flight appearance.

Otherwise, apart from the possible addition of Ayala, Karanka will be selecting from the same squad as Boro look to inflict a second straight defeat on Sunderland's new manager David Moyes.